Slurry-pumping means

ABSTRACT

A slurry-pumping means which comprises a driving pump, an intake diaphragm pump, an exhaust diaphragm pump connected therewith in series and an intermediate check valve, and driven by a fluid medium in such a manner that, while two unit volumes of the slurry are taken in by the intake diaphragm pump, one unit volume of the slurry contained in the exhaust diaphragm pump is exhausted out thereof, and, while the intake diaphragm pump does not take in the slurry, one unit volume previously taken in by the intake pump is exhausted from the exhaust pump and the other one unit volume previously taken in by the intake pump is accumulated in the exhaust pump and becomes the first-named one unit volume. By virtue of the above operating manner and a construction adapted thereto, the output becomes continuous with a uniform pressure. Various means for operation and maintenance thereof are also disclosed.

Q United States Patent [151 3,637,328 Kurokawa et al. [4 Jan. 25, 1972 [54] SLURRY.PUMPING MEANS 3,306,215 2/1967 Sebastiani ..417/246 2,437,341 3/1948 Aikman ..417/246 [72] inventors: Akitsugu Kurokawa; Shigeru Maezawa,

both of Yokohama 7 Primary Examiner- Robert M. Walker [73] Assignee: Kabushiki Kaisha lnouye Shokai (Inouye Anomey zachary T'wo-bensmnh'znd &C.,Ltd. Ykh ,J

am 57 ABSTRACT 22 Filed: June 24,1970

A slurry-pumping means WhlCh comprises a driving pump, an [2]] Appl. No.: 49,384 intake diaphragm pump, an exhaust diaphragm pump connected therewith in series and an intermediate check valve, and driven by a fluid medium in such a manner that, while two [30] Foreign Apphcauon Priority Data unit volumes of the slurry are taken in by the intake Feb. 26, 1970 Japan ..45/16119 diaphr gm p mp. n ni l m f h ry contained n Feb. 26, 1970 Japan. 45/18604 the exhaust diaphragm pump is exhausted out thereof, and,

Feb. 26, 1970 Japan..... ....45/l8605 while the intake diaphragm pump does not take in the slurry,

Feb. 26, 1970 Japan ..45/18606 ne unit volume previously taken in by the intake pump is exhausted from the exhaust pump and the other one unit volume [52] U.S. Cl ..417/246, 417/395, 417/900 previously taken in by the intake pump is accumulated in the [51] Int. Cl ..F04b 3/00, F04b 43/06, F04b 15/02 exhaust pump and becomes the first-named one unit volume. [58] Field of Search ..417/246, 339, 394, 395, 900 By virtue of the above operating manner and a construction adapted thereto, the output becomes continuous with a [56] References Cited uniform pressure. Various means for operation and maintenance thereof are also disclosed. UNITED STATES PATENTS 482,840 9/1892 Booth ..417/339 7 7 Drawing Figures a: 63 x 6 F I 22 2 49 =1, r :64 W p I I 47a- 4g :44

-43 7 IA I: g J04 PATENTEDJANZSIHYZ 3,637,328

- SHEI1UF 3 Fig.5

E XHAUST/NG WESSURE TIME INVENT AmTJ AKV'IQOICAW M4 5,4,; 0 MAEZAWA BY mama M25 :972 5.657.326 SHEET 20? 3 OOOOOOO INVENTORS AK: Ts CA Kwzo cA A M4 B H 65m) MAE'ZAWA 1 SLURRY-PUMPING MEANS BACKGROUND OF THE INVENTION v due to the start and interruption of the operation of a spray gun so that uneven operation occurs. When a reciprocating pump is used for such a purpose, even if an air chamber or an accumulator is employed with the double-acting pump, it is impossible to completely remove the pulsation inherent in the pump by virtue of the load variation. Furthermore, it is undesirable to pump a slurry by a pump having a sliding surface from the point of view of maintaining accuracy of pressure. Particularly, in pumping a coating material containing powdered metal such as aluminum, zinc, and the like or particles of such a substances as iron oxide, silica, and the like, it is improbable that a pumping means will have a long life due to the abrasion of the sliding surface by the coating material.

The primary object of this invention is to provide a slurrypumping means, of which the output is quantitatively uniform with a substantially uniform pressure without being affected by pulsation of the pumping means.

Another object of this invention is to provide a slurry-pumping means which has a simplified construction so as to facilitate cleaning, inspection, maintenance, repairs, and the like thereof.

Still another object of this invention is to provide a slurrypumping means comprising a pair of diaphragm pumps and a driving pump having a piston, which may be easily stopped at its neutral position for maintaining the diaphragm pumps in a proper condition.

Further, another object of this invention is to provide a slurry-pumping means, of which the level of fluid medium is easily inspected externally.

SUMMARY OF THE INVENTION Briefly stated in accordance with one aspect of this invention, there is provided a slurry-pumping means comprising a driving pum an intake, diaphragm pump, an exhaust diaphragm pump connected therewith in series an intermediate check valve and driven by a fluid medium in such a manner that the intake stroke and the exhaust stroke of the two diaphragm pumps are alternate with each other so that two unit volumes of the slurry are taken by the intake diaphragm pump during an intake stroke thereof, of which one unit volume is exhausted from the exhaust diaphragm pump during the subsequent exhaust stroke of the intake diaphragm pump and the other one unit volume is exhausted from the exhaust diaphragm pump during the subsequent intake stroke of the intake diaphragm pump. By virtue of the above operation and construction, the output of the exhaust diaphragm pump becomes substantially continuous with a uniform pressure.

BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood and other objects and additional advantages of the invention will become apparent upon perusal of the following description taken in connection with the drawings, in which:

FIG. 1 is a schematic view of a slurry-pumping means embodying this invention;

FIG. 2 is a vertical central sectional view thereof;

FIG. 3 is an enlarged partly sectional elevation of a controlling valve thereof;

FIG. 4 is an enlarged cross-sectional view thereof;

FIG. 5 is a graph showing a pulsation in the output pressure of the slurry-pumping means;

FIG. 6 is a schematic view of another slurry-pumping means embodying this invention; and

FIG. 7 is a schematic view of a modification thereof. Similar numerals refer to similar parts throughout the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring more particularly to the drawings, the preferred embodiments of this invention will now be described; however, this description will be understood to be illustrative of the invention and not as limiting it to the particular constructions as shown and described. There is shown a slurry-pumping means comprising two diaphragm pumps 11 and 12 incorporated with a driving pump 40 and adapted to be driven a fluid medium. The two diaphragm pumps 11 and 12 are connected in series and have the same capacity, they are provided with slurry chambers 13 and 14 surrounded by cylindrical expansible diaphragms 15 and 16 having annular corrugations 29 for furthering the expansibility thereof. The intake slurry chamber 13 is connected to a slurry reservoir 19. An intake valve 20 is interposed between the intake slurry chamber 13 and the slurry reservoir 19. The intake'slurry chamber 13 is connected also to the exhaust slurry chamber 14. An exhaust valve 21 is interposed between the two slurry chambers 13 and 14. The exhaust slurry chamber 14 is connected to, for example, a spray gun 22. These valves 20 and 21 are check valves.

The cylindrical expansible diaphragms l5 and 16 are surrounded by fluid medium chambers 17 and l8,'respectively. The intake fluid medium chamber 17 is connected to a space 23 under a second piston 27 inside a second cylinder 30 through a passage 24. The exhaust fluid medium chamber 18 is connected to a space 25 above the second piston 27 inside the second cylinder 30 through a passage 26. The two diaphragm pumps 11 and 12 are adapted to be alternately inflated by reciprocation of the second piston 27, when the two fluid medium chambers 17 and 18, two connecting passages 24 and 26, and two spaces 23 and 25 are filed with a fluid medium.

The valve body of the intake valve 20 is detachably screwed down on the bottom of the intake slurry chamber 13 by a nut 28 for facilitating cleaning. The valve body of the exhaust valve 21 is detachably screwed down on the bottom end of a sleeve 36 arranged coaxially with and inside the exhaust slurry chamber 14. A cap 35 is screwed down in a hold formed in the top of the exhaust slurry chamber 14 and adapted to keep the exhaust valve 21 in place intermediate the sleeve 36. The sleeve 36 is formed with a plurality of radial perforations 31 and surrounded by a strainer 32. The exhaust valve 21 constituted as above may be easily detached by unscrewing the cap 35 from the exhaust slurry chamber 14 for facilitating cleaning. Numeral 33 denotes a passage connecting the exhaust slurry chamber 14 with the outlet 34 when the pressured slurry is directed to, for example, a spray gun 22.

The driving pump is a pneumatic driving pump 40 comprising a cylinder 41 and a piston 42 adapted to be reciprocated inside the cylinder 41. The cylinder 41 is coaxially integrated with the second cylinder 30 and arranged thereon. A piston rod 37 of the second piston 27 is extended through a wall between the two cylinders 30 and 41 and fixed to the piston 42 so that the two pistons 27 and 42 are integrally reciprocatory. A piston rod 47 is further upwardly extended coaxially with the cylinder 41 from the piston 42 to the interior of a controlling valve 60 for controlling the pneumatic driving pump 40, which is arranged on the top of the cylinder 41. A housing 61 of the controlling valve 60 is coaxially fixed to the cylinder 41. A spool 62 is slidably carried in the housing 61 coaxially therewith. The housing 61 is provided with two air-connecting holes 63 and 64 and an air inlet 65 through the wall thereof. One air-connecting hole 63 in the upper side of the housing 61 is connected with the lower side space 43 of the cylinder 41 under the piston 42 by a pipe 46 and the other hole 64 of the two air-connecting holes in the lower side of the housing 61 is connected with the upper side space 44 of the cylinder 41 above the piston 42 by another pipe 45. The air inlet 65 is in the center of the distance between the two air-connecting holes 63 and 64.

The spool 62 is formed with five lands, which are axially symmetrically arranged. The central land is an air intake land 70, of which the axial length b is long enough to cut off air intake through the air inlet 65 when the spool 62 is brought to its neutral position and the diameter is denoted by D in FIG. 3. A pair of first guiding lands 73 and 74 having the same diameters as the air intake land 70 are arranged above and below it leaving the same spaces 71 and 72 from each other, respectively. A pair of second guiding lands 77 and 78 having the same diameters D as the air intake land 70 are arranged above the first guiding land 73 and below the first guiding land 74 leaving the same spaces 75 and 76 from each other, respectively. A pair of exhaust lands 81 and 82 having the same diameters d each other, which are shorter than D, are arranged above the second guiding land 77 and below the second guiding land 78 leaving the same spaces 79 and 80 from each other, and adapted to be brought out of the axial extremities of the housing 61 respectively. A pair of radially internally and externally flanged stoppers 83 and 84 are formed on the endmost surfaces of the exhausting lands 81 and 82, respectively. The first guiding lands 73 and 74 and the second guiding lands 77 and 78 are formed with a number of, for example, six, axial flutes 85 in the peripheral surfaces thereof in alignment with each other.

The piston rod 47 is coaxially extended into a coaxial bore formed inside the spool 62. An upper washer 90 and a lower washer 91 are freely mounted on the top end of the piston rod 47. A coil spring 92 is also freely mounted between the two washers 90 and 91 on the piston rod 47. The two washers 90 and 91 are adapted to be brought into engagement with the stoppers 83 and 84 so as to move the spool 62 axially during certain parts of a cycle of the operation of the driving pump 40, respectively.

in FIGS. 2 and 3, and the driving pump 40 and the controlling valve 60 are illustrated in the neutral position. Practically speaking, if the operation of the slurry-pumping means is interrupted, the spool 62 is lowered apart from the neutral position by gravity. Under these circumstances, when compressed air is admitted into the air inlet 65, the upper air-connecting hole 63 is supplied with compressed air through the annular space 71, flutes 85 of the upper first guiding land 73, annular space 75, flutes of the upper second guiding land 77, and annular space 79, so that the compressed air is admitted into the space 43 under the piston 42 through a pipe 46 to lift the piston 42. At the same time, air contained in the space 44 on the piston 42 is exhausted through a pipe 45, the lower airconnecting hole 64, annular space 76, flutes 85 of the lower second guiding land 78, annular space 80, and an annular gap 86 formed between the exhaust land 82 and the lower end of the housing 61. When the piston 42 approaches the upper end of its lifting stroke, the upper washer 90 pushes up the radially internally flanged stopper 83 of the spool 62 so as to slide it upwardly into the neutral position. When the spool 62 is brought into its neutral position, the intake of the compressed air through the air inlet 65 into the space 43 for lifting the piston 42 is interrupted.

The piston 42 is lifted by inertia, so that the spool 62 is also lifted across the neutral position, and therefore, the feed of compressed air introduced from the air inlet 65 and directed to the upper air-connecting hole 63 is changed over from the air inlet 65 to the lower air-connecting hole 64. Thus the space 44 above the piston 42 is supplied with compressed air introduced through the pipe 45 so as to lower the piston 42, while the compressed air contained in the space 43 is expelled through the pipe 46, upper air-connecting hole 63, and an annular exhausting gap 87.

When the spool 62 is lifted from its neutral position, the pressure of the compressed air acting on the spool 62 for lifting it is a differential pressure P due to the action of the air on the air intake land 70 and the exhaust land 82, which is represented by the equation Pa 17/4 X (D -f) in which p represents the pressure of the intake compressed air. By virtue of the differential pressure P the spool 62 is lifted faster than the lift of the piston rod 47. Thus the stopper 84 of the spool 62 is brought into engagement with the lower end of the housing 61 and, at the same time, the lower air-connecting hole 64 is closed by the lower exhausting land 82, so that any leakage of the compressed air through the lower annular exhausting gap 86 from the interior of the housing 61 is completely restrained. Thus the spool 62 is kept in its uppermost position by the pressure of the compressed air without any occurrence of instability of the spool itself until it is subsequently lowered by the action of the piston 42. When the stoppers 83 and 84 of the spool 62 are broughtinto engagement with the upper and lower washers and 91 after the spool 62 has been placed in its uppermost and lowermost positions as above, respectively, the coil spring 92 acts the part of a buffer and, in addition, when the piston 42 is slowly moved, and therefore, it is probable that the spool 62 does not pass the neutral position by the action of inertia only, but the spool 62 is accelerated by the action of the spring 92. That is to say, when the washers 90 and 91 approach their endmost positions, respectively, the coil spring 92 is compressed by the differential pressure P. When the spool 62 passes its neutral position, and therefore, the introduction of compressed air to one air-connecting hole is changed over to the other air-connecting hole, the compressed coil spring 92 is released from the differential pressure P, and therefore, the spool 62 is positively slid through its neutral position. By virtue of this construction, the reversing motion of the piston 42 at its endmost positions is remarkably hastened, and therefore, the variation in output of the slurry-pumping means, which corresponds to the reversing motion, is minimized, as shown in FIG. 5.

When the piston 42 is reciprocated by the compressed air controlled by the controlling valve 60, it is to be understood that the second piston 27 is also reciprocated in the second cylinder 30 corresponding to the first-named reciprocation. The two diaphragm pumps 11 and 12 are operated by the action of the second piston 27 as described hereinbefore. In accordance with this invention, it is necessary to determine the interrelation of an inner diameter R of the second cylinder 30 to a diameter r of the piston rod 37 of the second piston 27 as follows:

By adopting the interrelation, the fluid medium delivered through the lower connecting passage 24 during one lowering stroke of the second piston 27 becomes double that delivered through the upper connecting passage 26 during one lifting stroke of the second piston 27, and therefore, the pumping action of the intake diaphragm pump 11 becomes double in volume of that of the exhaust diaphragm pump 12.

in this case, the fluid medium contained in the upper space 25 is pushed by the lifting second piston 27 with a pressure P,,, which is represented by the equation 1T 71' ,2) 4 (4 in which F re$iii2 force whereby thFsESfiFfiiston 27 is moved. Subsequently, the fluid medium contained in the lower space 23 is pushed by the lowering second piston 27 with a pressure P,,, which is represented by the equation Hence hausted from the exhaust slurry chamber 14 to the outlet 34 and the other half of the volume is accumulated in the exhaust slurry chamber 14, when the second piston 27 is lowered. When the second piston 27 is again lifted, a volume of slurry is again taken in the intake slurry chamber 13 from the reservoir 19 and at the same time the accumulated volume is exhausted to the outlet 34 continuously from the preceding output. Thus the exhaust slurry chamber 14 has the same volume as that of the intake slurry chamber 13 in spite of the volume of the upper connecting passage 26 so the structure, acts the part of an accumulator and air chamber, and the slurry-pumping means in accordance with this invention is simplified in construction.

There is a necessary requirement in the slurry-pumping means comprising diaphragm pumps adapted to be driven by means of a fluid medium, that mechanism is provided to stop it in the neutral position. When the fluid medium is first supplied into the two fluid medium chambers 17 and 18 and the two spaces 23 and 25 of the second cylinder 30, it is necessary to stop the slurry-pumping means in the neutral position. Otherwise, if the second piston 27 is stopped in the lowermost position, an excessive volume of the fluid medium is supplied into the exhaust fluid medium chamber 18 and the upper space 25 of the second cylinder 30 so as to be confined therein, while a small volume of the fluid medium is supplied to the intake fluid medium chamber 17 and the lower space 23 of the second cylinder 30. This is so because the diaphragms 15 and 16 are not positively deformed but neutrally positioned due to communication with the atmosphere as described hereinafter. When the second piston 27 is lifted after the feed of the fluid medium as above, the exhaust diaphragm 16 is excessively internally inflated and the intake diaphragm 15 is excessively externally inflated at their neutral positions. Such deviated neutral positions of the diaphragms 15 and 16 cause trouble.

Furthermore, if the fluid medium leaks, it is necessary to replenish the fluid medium at once to prevent the diaphragms from moving to the deviated positions. For replenishment, it is also necessary to stop the slurry-pumping means in the neutral position. If the positions of the diaphragms 15 and 16 have been deviated, it is necessary to correct the positions to the true neutral ones before replenishment.

To stop the second piston 27 in the true neutral position, there is provided a bearing member 49 on the outer side of the housing 61, which supports a vertically swingable lever 51. A radial hole is formed in the lower end of the spool 62, in which a fitting or latch member 52 is radially slidably inserted. A spring 53 is compressed between a flange of the fitting member 52 and the spool 62 so as to normally keep the inner end of the fitting member 52 out of its engagement with the piston rod 47 extended the bore of the spool 62. A leaf spring 54 is arranged on the lower side of the swingable lever 51 and adapted to be inserted between the lower side and the outer end of the fitting member 52 radially outwardly spring loaded as above. Thus the fitting member 52 may be radially inwardly slid against the piston rod 47 by turning the swingable lever 51 into its active position as shown by solid line in FIG. 2. An annular groove 48 is circumferentially formed on the piston rod 47, which is adapted to receive the inner end of the fitting member 52 and brought into engagement therewith, and arranged in a position corresponding to the neutral position of the piston 42, and it is possible to stop the reciprocation of the piston 42 in its neutral position, where the air inlet 65 in the housing 61 is completely closed by the air intake land 70 of the spool 62 as shown in FIGS. 2 and 3, by manually lowering the swingable lever 51 into its active position.

For supplying the fluid medium into the slurry-pumping means, at first the swingable lever 51 is manually turned down into its active position. Subsequently, the slurry-pumping means itself is laid right side down in FIG. 2 so as to bring the axis of the means into the horizontal position. There are two plugs 57 and 58 screwed down in respective holes formed in the upper side of the horizontally positioned slurry-pumping means. The two fluid medium chambers 17 and 18 and the two diaphragms 15 and 16 are exposed to the atmosphere as described hereinbefore, by unscrewing the two plugs 57 and 58, and therefore, the two diaphragms 15 and 16 recover their neutral positions by virtue of their self-forming forces. It is to be noted that the second piston 27 is kept in its neutral position. Under these circumstances, it is now possible to replenish the two fluid medium chambers 17 and 18, two connecting passages 24 and 26, and two spaces 23 and 25 of the second cylinder 30, with proper volumes of the fluid medium, respectively. After the replenishment of the fluid medium, the two plugs 57 and 58 are screwed down and the slurry-pumping means is again set in its upstanding position. Of course, the swingable lever 51 is to be turned up into its inactive position before the actuation of the slurry-pumping means.

When the swingable lever 51 is brought into its active position, the compressed air input to the inlet 65 is throttled by a valve means (not shown). During the time piston rod 47 is moving out of its neutral position, the fitting member 52 is not brought into engagement with the annular groove 48, and therefore, the fitting member 52 is further inwardly loaded by the leaf spring 54 so that, when the piston rod 47 passes its engaging position with the fitting member 52, it is at once brought into engagement with the annular groove 48. After engagement, the piston rod 47 is slid relatively to the cylinder 41, together with the spool 62, which is slid relatively to the housing 61. When the piston rod 47 arrives at its neutral position, which corresponds to the neutral position of the spool 62 where the air inlet 65 is completely closed by the air intake land 70, the piston rod 47 is completely stopped together with the spool 62.

In accordance with this invention, a fluid medium leakagedetecting means is provided. Such leakage occurs at the following two points: one point is the clearance between the second piston 27 and the inner wall of the second cylinder 30 or around an O-ring 101 mounted on the periphery of the second piston 27 and the other is the clearance between the second piston rod 37 and the wall between the two cylinders 30 and 41. In this connection it is to be considered that it is inevitable and significant that the O-ring 101 is worn by operation. By leakage at the former point, the pumping action of the second piston 27 deteriorates and the output during the lifting and lowering strokes is reduced. By leakage at the latter point, the output during the lifting stroke is reduced. Particularly, the diaphragms l5 and 16 are disadvantageously affected by the leakage. The neutral positions of the diaphragms l5 and 16 are deviated to positions where the diaphragms 15 and 16 are inflated by the differential volumes of the fluid medium clue to the one-sided leakage thereof, while continuously repeating the expansion and contraction, tending to cause breakage of the diaphragms 15 and 16. l-leretofore, it has been practically impossible to use the diaphragm pump under a pressure higher than about 5 kg./cm. mainly due to the above described action. Although various proposals for surmounting the drawback have been known, it has been impossible to be practically satisfied by these proposals.

The fluid medium leakage-detecting means in accordance a hole this invention comprises a fluid medium reservoir 102 arranged inside the top wall of the second cylinder 30. The fluid medium reservoir 102 communicates with the clearance between the second piston rod 37 and the wall between the two cylinders 30 and 41 by a passage 103, which is opened in the clearance between two O-rings 104 mounted on the inner surface of a hole formed in the wall. The outer end of the fluid medium reservoir 102 is closed off by a transparent plate 105 in a fluidtight manner, whereby it is possible to externally inspect and detect any variation in level of the fluid medium or any leakage thereof. I

Reference is now made to FIG. 6 illustrating a modification of the slurry-pumping means in accordance with this invention. In this modification, an intake diaphragm pump 11 has a double capacity of the exhaust diaphragm pump 12. During the lifting stroke of the second piston 27, two unit volumes of a slurry are taken into the intake slurry chamber 13 and, at the same time, one unit volume of the slurry contained in the exhaust slurry chamber 14 is exhausted out thereof toward, for example, a spray gun 22. Subsequently, during a lowering stroke of the second piston 27, the two unit volumes are exhausted from the intake slurry chamber 13 through the valve 21, of which one unit volume is exhausted from the exhaust slurry chamber 14 toward the spray gun 22 continuously from the preceding output and the other one unit volume is transferred into the exhaust slurry chamber 14 and retained therein.

Reference is now made to FIG. 7 illustrating still another modification of the slurry-pumping means in accordance with this invention. In this modification, a rotary pump is substituted for the reciprocating driving pump 40, which comprises a casing 111 and an eccentric rotor 112. An annular space between the inner periphery of the casing 111 and the eccentric rotor 112 is divided into a major chamber 113 and a minor chamber 114 by means of two expansion partitions 115. The major chamber 113 communicates with the fluid medium chamber 17 of the intake diaphragm pump 11 through a passage 117 and the minor chamber 114 communicates with the fluid medium chamber 18 of the exhaust diaphragm pump 12 through a passage 118. The outputs of these two passages 117 and 118, which alternate with each other, are so allotted as to be two unit volumes versus one unit volume, and therefore, when the two chambers 113 and 114, the two passages 117 and 118, and the two fluid medium chambers 17 and 18 are filled with a fluid medium and the eccentric rotor 112 is rotated by, for example, an electric motor (not shown), the slurry-pumping means is operated similarly to the described preceding embodiment.

The cylindrical diaphragm shown in the first and third embodiments is capable of being adapted to an output, which is larger than that of a disk diaphragm, as shown in H0. 6, with a size of the same extent as the former, and therefore, the cylindrical diaphragm is more advantageous than the disk diaphragm in order to make a small slurry-pumping; means and adapted to a higher pressure.

While particular embodiments of the invention have been illustrated and described, further modifications thereof will readily occur to those skilled in the art. It should be understood therefore that the invention is not limited to the particular constructions disclosed but that the appended claims are intended to cover all modifications which do not depart from the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A slurry-pumping means comprising driving pump means and two diaphragm pump means said diaphragm pump means comprising an inlet, a check valve, an intake diaphragm pump, another check valve, an exhaust diaphragm pump, and an outlet, connected together and in series, said diaphragm pump means being adapted to be driven by said driving pump, by using a fluid medium in such a manner that intake strokes and exhaust strokes of the two diaphragm pumps are alternate with each other so that two unit volumes of slurry are taken in by the intake diaphragm pump during an intake stroke thereof, of which one unit volume is exhausted from said exhaust diaphragm pump during the subsequent exhaust stroke of said intake diaphragm pump and the other one unit volume is exhausted out of said exhaust diaphragm pump during the subsequent intake stroke of said intake diaphragm pump, so that output of said diaphragm pump means is substantially continuous with a uniform pressure, said driving pump being pneumatically driven and comprising a cylinder, a piston and a controlling valve,

said controlling valve including a housing and a spool,

said housing being arranged coaxially on and fixed to said cylinder, and formed with an upper air-connecting hole connected to a space above said piston, a lower air-connecting hole connected to another space under said piston, and an air inlet in the center of the axial distance between the said two air-connecting holes,

said spool being arranged coaxially inside and freely slidable relatively to said housing, and formed with a central coaxial bore, an air intake land adapted to cut off said air inlet when said piston is brought to its neutral position, four guiding lands arranged symmetrically above and below said air intake land and having the same diameter as said air intake land and a number of axial external flutes, respectively, two exhausting lands arranged symmetrically above and below said air intake land and having the same diameter as said air intake land and a number of axial external flutes, respectively, two exhausting lands arranged symmetrically above and below said guiding lands and having a diameter shorter than said guiding lands diameter, respectively, and two radially internally and externally flanged stoppers formed on the endmost surfaces of said exhausting lands,

said piston having a piston rod extended into said bore and having two washers axially freely mounted on the upper end of said piston rod and a coil spring axially freely mounted on said upper end and arranged between said two washers,

said spool being adapted to be axially slid by said piston when said washers are brought into engagement with said stoppers.

2. A slurry-pumping means as claimed in claim 1 in which said intake diaphragm pump has a cylindrical intake slurry chamber and said exhaust diaphragm pump has a cylindrical exhaust slurry chamber.

3. A slurry-pumping means as claimed in claim I, in which said driving pump further comprises a neutrally positioning means comprising a vertically swingable lever supported on said housing, a fitting member radially slidably mounted in said spool, and an annular groove formed on said piston rod,

said swingable lever being adapted to slide said fitting member inwardly regardlessly of relative position of said housing to said spool, and

said fitting member being adapted to be brought into engagement with said annular groove when the former is inwardly slid,

whereby said piston is stopped in its neutral position by manual operation of said swingable lever, where said washers are not in engagement with said stoppers and which corresponds to a position where said air inlet is completely cut off by said air intake land and to the neutral position of said set of two diaphragm pumps.

4. A slurry-pumping means as claimed in claim 1, in which said intake diaphragm pump and said exhaust diaphragm pump have fluid medium chambers containing said fluid medium, respectively, and

a fluid medium leakage-detecting means is provided, which comprises a fluid medium reservoir arranged inside a wall between two cylinders containing said piston and another piston integrated therewith for driving said fluid medium, respectively, adapted to be communicated with said fluid medium chambers, and having an outer end walled by a transparent plate in a fluidtight manner.

5. A slurry-pumping means as claimed in claim 4, in which said fluid medium chambers are provided with fluid medium replenishing holes arranged in a wall of said diaphragm pumps, on the opposite side to said another piston, and adapted to be closed by plugs, respectively.

6. A slurry-pumping means as claimed in claim 1, in which said driving pump is a rotary pump comprising a casing, an eccentric rotor, and an annular space between said casing and said eccentric rotor,

said annular space being divided into a major chamber communicated with a slurry chamber of said intake diaphragm pump and a minor chamber connected with another slurry chamber of said exhaust diaphragm pump.

7. A slurry-pumping means as claimed in claim 1 in which said intake diaphragm has a cylindrical intake slurry chamber and said intake slurry chamber, so as to act also as an accumulator and an air chamber. 

1. A slurry-pumping means comprising driving pump means and two diaphragm pump means said diaphragm pump means comprising an inlet, a check valve, an intake diaphragm pump, another check valve, an exhaust diaphragm pump, and an outlet, connected together and in series, said diaphragm pump means being adapted to be driven by said driving pump, by using a fluid medium in such a manner that intake strokes and exhaust strokes of the two diaphragm pumps are alternate with each other so that two unit volumes of slurry are taken in by the intake diaphragm pump during an intake stroke thereof, of which one unit volume is exhausted from said exhaust diaphragm pump during the subsequent exhaust stroke of said intake diaphragm pump and the other one unit volume is exhausted out of said exhaust diaphragm pump during the subsequent intake stroke of said intake diaphragm pump, so that output of said diaphragm pump means is substantially continuous with a uniform pressure, said driving pump being pneumatically driven and comprising a cylinder, a piston and a controlling valve, said controlling valve including a housing and a spool, said housing being arranged coaxially on and fixed to said cylinder, and formed with an upper air-connecting hole connected to a space above said piston, a lower air-connecting hole connected to another space under said piston, and an air inlet in the center of the axial distance between the said two air-connecting holes, said spool being arranged coaxially inside and freely slidable relatively to said housing, and formed with a central coaxial bore, an air intake land adapted to cut off said air inlet when said piston is brought to its neutral position, four guiding lands arranged symmetrically above and below said air intake land and having the same diameter as said air intake land and a number of axial external flutes, respectively, two exhausting lands arranged symmetrically above and below said air intake land and having the same diameter as said air intake land and a number of axial external flutes, respectively, two exhausting lands arranged symmetrically above and below said guiding lands and having a diameter shorter than said guiding lands'' diameter, respectively, and two radially internally and externally flanged stoppers formed on the endmost surfaces of said exhausting lands, said piston having a piston rod extended into said bore and having two washers axially freely mounted on the upper end of said piston rod and a coil spring axially freely mounted on said upper end and arranged between said two washers, said spool being adapted to be axially slid by said piston when said washers are brought into engagement with said stoppers.
 2. A slurry-pumping means as claimed in claim 1 in which said intake diaphragm pump has a cylindrical intake slurry chamber and said exhaust diaphragm pump has a cylindrical exhaust slurry chamber.
 3. A slurry-pumping means as claimed in claim 1, in which said driving pump further comprises a neutrally positioning means comprising a vertically swingable lever supported on said housing, a fitting member radially slidably mounted in said spool, and an annular groove formed on said piston rod, said swingable lever being adapted to slide said fitting member inwardly regardlessly of relative position of said housing to said spool, and said fitting member being adapted to be brought into engagement with said annular groove when the former is inwardly slid, whereby said piston is stopped in its neutral position by manual operation of said swingable lever, where said washers are not in engagement with said stoppers and which corresponds to a position where said air inlet is completely cut off by said air intake land and to the neutral position of said set of two diaphragm pumps.
 4. A slurry-pumping means as claimed in claim 1, in which said intake diaphragm pump and said exhaust diaphragm pump have fluid medium chambers containing said fluid medium, respectively, and a fluid medium leakage-detecting means is provided, which comprises a fluid medium reservoir arranged inside a wall between two cylinders containing said piston and another piston integrated therewith for driving said fluid medium, respectively, adapted to be communicated with said fluid medium chambers, and having an outer end walled by a transparent plate in a fluidtight manner.
 5. A slurry-pumping means as claimed in claim 4, in which said fluid medium chambers are provided with fluid medium replenishing holes arranged in a wall of said diaphragm pumps, on the opposite side to said another piston, and adapted to be closed by plugs, respectively.
 6. A slurry-pumping means as claimed in claim 1, in which said driving pump is a rotary pump comprising a casing, an eccentric rotor, and an annular space between said casing and said eccentric rotor, said annular space being divided into a major chamber communicated with a slurry chamber of said intake diaphragm pump and a minor chamber connected with another slurry chamber of said exhaust diaphragm pump.
 7. A slurry-pumping means as claimed in claim 1 in which said intake diaphragm pump has a cylindrical intake slurry chamber and said exhaust diaphragm pump has a cylindrical exhaust slurry chamber, which has the same capacity with that of and is connected with and arranged vertically in series above said intake slurry chamber, so as to act also as an accumulator and an air chamber. 